Saving fuel is a key concern for airlines, and one of the main reasons United and other carriers have switched over to lighter seats on some aircraft.

Those seats, made by Germany's Recaro, have the extra advantage of being thinner than conventional options, so rows can be closer together and more paying passengers can be packed onboard.

Now, three young French guys have upped the ante with a seat that's nearly three times lighter than Recaro's.

Benjamin Saada, Jean-Charles Samuelian, and Vincent Tejedor created Expliseat in 2011 and have now started selling it. Made from titanium and composites, it weighs just 4 kg (8.8 lbs). The Recaro seats used by United weigh 11 kg.

The difference is enough to cut fuel consumption to the tune of up to $400,000 per plane per year, the company says. If that's right, putting these seats on all 300 of Ryanair's 737-800 jets could save the budget airline about $120 million a year.

The seat, which consists of just 30 parts and is "pre-reclined" by 18 degrees, is designed for use in the Boeing 737 and Airbus A320 family of aircraft. Those are the most popular planes for short- and medium-haul flights and represent a huge market potential.

In March, the European Aviation Safety Agency approved the seat for commercial use. That same month, the startup signed its first customer. It will provide 220 seats for an A321 flown by charter airline Air Méditerranée, according to French newspaper LesEchos.